1. Field of the Invention
The present invention relates to a honeycomb structure.
2. Discussion of the Background
Recently, particulate matters (hereinafter, also simply referred to as particulates), that are contained in exhaust gases discharged from internal combustion engines of vehicles, such as buses and trucks, and construction machines and the like, have raised serious problems as those particulates are harmful to the environment and the human body.
For this reason, various applications in which honeycomb structures, which are made from porous ceramics using silicon carbide, cordierite or the like as materials, are used as filters for capturing particulates in exhaust gases to purify the exhaust gases have been proposed.
With respect to the honeycomb structure of this kind, as shown in FIG. 6, a cylindrical-shaped honeycomb structure 30 having a plurality of cells 31 longitudinally (direction shown by an arrow D in FIG. 6(a)) placed in parallel with one another with a cell wall 33 therebetween has been known. As shown in FIG. 6(b), the cell 31 is sealed at either one of end portions on a flow-in side or a flow-out side of exhaust gases by a plug 32 so that exhaust gases flowing into one cell 31 surely pass through the cell wall 33 to flow out from another cell 31. In other words, when the honeycomb structure 30 is installed in an exhaust gas flow path of an internal-combustion system, particulates in exhaust gases discharged from the internal combustion system are captured by the cell walls 33 upon passing through the honeycomb structure 30 so that the exhaust gases are purified.
WO2004/024294 A discloses the honeycomb structure of this kind, in which cells (hereinafter, also referred to as flow-in side cells), each having a sealed end portion on the flow-out side of exhaust gases, are prepared as cells with a large volume (hereinafter, also referred to as large-volume cells), and cells (hereinafter, also referred to as flow-out side cells), each having a sealed end portion on the exhaust-gas flow-in side, are prepared as cells with a small volume (hereinafter, also referred to as small-volume cells) so that an aperture ratio on the flow-in side of exhaust gases is made relatively greater than the aperture ratio on the flow-out side of exhaust gases.
Moreover, with respect to an exhaust-gas purifying apparatus in which a catalyst is supported on cell walls of the honeycomb structure, Japanese Unexamined Patent Application Disclosure No. 2001-207836 A discloses an exhaust-gas purifying apparatus of an internal combustion system in which: a honeycomb filter having a plurality of cells formed therein is provided, and fine pores allowing exhaust gases to pass through are formed in each cell wall between mutually adjacent cells, a catalyst substance is supported inside the cell walls of the honeycomb filter, and the catalyst substance is distributed so as to be supported on the flow-in side of exhaust gases passing through the cell wall in an amount comparatively larger than that of the catalyst substance supported on the flow-out side. The contents of WO2004/024294 A and Japanese Unexamined Patent Application Disclosure No. 2001-207836 A are incorporated herein by reference in their entirety.